Electric furnace system



April 1934- E. F. CHRISTENSEN ELECTRIC FURNACE SYSTEM Filed July 15, 1933 Fig.2.

2 4 m FFE W p 6 m [w% w b [WW a Everett F Chri'stensen His ttohney.

Patented Apr. 24, 1934 UNITED STATES ELECTRIC FURNACE SYSTEM Everett F. Christensen, Pittsfleld, Mass., assignor to General Electric Company, a corporation of New York Application 15, 1933, Serial No. 680,565

3Claims.

My invention relates to electric furnace systerns, more particularly to polyphase arc furnace systemssuch as used in the melting of metals, wherein current is supplied through transformers to the furnace, and has for its object a system 5 of this character having simplified switching means for applying different selected voltages to the furnace with different selected values of reactance in the circuit.

At thepresent time are furnaces are most frequently built to give a balanced load on existing high voltage supply circuits which are commonly three phase. By means of transformers the voltage is reduced to a value suitable for the furnace, and furthermore in accordance with prior practice suitable switching means is provided whereby the connections of the primary windings of the transformers may be changed from Y to delta or connections made to different taps on the primary windings to apply different selected voltages to the furnace as required for most expeditious operation as the melting operation proceeds. Reactance is also included in the circuit with the primary windings to prevent violent current surges, and it is customary to change the value of this reactance which is varied in conformity with the variations in voltage.

It is a primary object of my invention to provide simple and inexpensive switching means for changing both the voltage supplied to the furnace and the reactance in the furnace circuit.

In carrying out my invention in one form I provide a pair of reactance coils for each primary winding. together with simplified switching means for changing the primary connections and for selectively includingthe reactance coils or portions thereof in the primary circuit. The delta connection of the primary windings is made through one of the coils of each of the pairs, while the Y-connection of the primary windings is made through the other coils.

, For a more complete understanding of my invention, reference should be had to the accompanying dr'wing, Fig. 1 of'which shows in diaic form an arc furnace control system embodying my invention and wherein provision of metals. The furnace is provided with three carbonaceous electrodes 11, 12 and 13 which are vertically adjustable by suitable means, not shown. Furthermore, a suitable regulating means may be provided for adjusting the 'elec-' trodes in response to the current in the electrode circuits so as to maintain predetermined current values.

The three electrodes are supplied with current from suitable high voltage three-phase supply mains 14, 15 and 16, which are connected to the electrodes through sets of primary and secondary transformer windings 17, 18 and 19. The secondary windings of these transformers are preferably connected permanently to the electrodes either in Y, as shown or in delta. Preferably the three sets of windings 17, 18 and 19 areembodied in a three phase transformer, i. e. are mounted on a common magnetic core, although if desired, three single phase transformers may be used.

For the purpose of suitably varying the voltage applied to the furnace the primary windings of the transformer are provided with a plurality of taps, and selective switching mechanisms 20. 21 and 22 are provided respectively for the primary windings for selecting different primary taps and also for changing the primary connections from Y to delta.

For the purpose of damping out current surges during the operation of the furnace I also provide three reactors 23, 24 and 25 for the respective primary transformer windings. Each of these reactors is provided with two separate reactance windings or coils. As shown, the reactor 23 is provided with the "coils 28 and 29, these coilsbeing mounted on a magnetic core 30. Each cell is furthermore provided with a plurality of taps, as showmand two selected taps from each coil are connected through suitable conductors to suitable points on the selector switch 20. The reactors 24 and 25 are identical in construction with the reactor 23 and are provided with taps, two of which are connected in like manner to their respective selector switches 21 and 22. Preferably the three 100 sets of reactor windings are embodied in a three phase reactor, 1. e. mounted on a common magnetic core, although three separate magnetic cores may be used as shown.

In the operation of the selector switches 20. 105 21 and 22, one only of the coils of each re actor is used when connecting the transformer primary windings in delta, while the other windingsonlyofthereactorsareutilircdwiththe, Y connection between the primary windings. 1

For the purpose of facilitating the delta connection the upper terminal of the reactor coil 28 is connected through a conductor 30a directly to'the supply main 16, the upper terminal of the corresponding coil 31 of the reactor 24 is connected through a conductor 32 to the supply main 14, while the corresponding reactor coil 33 of the reactor 25 is connected through a conductor 34 to the supply main 15. Furthermore to facilitate the Y connection the upper terminals of the remaining reactor coils 29, 35 and 36 are connected to each other through a conductor 37. In other words, it will be observed that the reactor coils 28, 31 and 33 are permanently connected in a partial delta connection while the reactor coils 29, 35 and 36 are permanently connected in a partial Y connection. Preferably, the delta connected coils have higher reactance values than the others. This may be effected by providing a greater number of turns in these coils.

Preferably the three selector switches 20, 21 and 22 are mechanically or otherwise connected together so that they may be operated simultaneously to their respective positions. For example, the rotatable bridging members 40, 41 and 42 of the selector switches may be mounted in electrically insulating relation therewith on a common operating shaft, not shown. Each selector switch furthermore is provided with a plurality of pairs of spaced stationary contacts which are mounted in suitable positions about,

7 the center of rotation of the bridging member so as to be selectively engaged and connected together thereby. Since the selector switch, the reactor coils and the connection for all three primary windings are identical the connection established by only one switch, i. e., the selector 20, will be described in detail.

With the selector switches in the positions indicated in the drawing, the primary windings are connected in delta relation with each other to give a high voltage for the furnace. As shown, the bridging member 40 is in position to electrically connect together the pair of spaced stationary contacts 43, whereby a circuit is established through the conductor 44 from a selected tap on the primary of the transformer 17 through the bridging contact 40, a conductor 45, to a selected tap on the reactor coil 28, and thence through the reactor coil and the conductor 30a to the supply main l6. Similar connections are established bythe bridging members 41 and 42 for the primary windings of the transformers 18 and 19.

In order to obtain another voltage with delta connected primaries thefselector switches may be turned from the positions indicated in the drawing into engagement with the next pair of stationary contacts. In that position the bridging member 40 connects together the pair of contacts 48, thereby establishing a circuit through a conductor 49 from another selected tap on the primary winding of the transformer 17, and since this tap connects into the circuit a smaller portion of the primary winding than when the bridging member was in engagement with the contacts 43 it will be observed that a higher secondary voltage will be obtained. From the conductor 49 the circuit leads through the bridging member to a conductor 50, thence through a smaller portion of the reactance coil 28 and the conductor 30a to the supply main 16. Similar connections are established at the same time for the primaries of transformer 18 and 19 by the switches 21 and 22.

For the Y connections of the primary windings the selector switches are turned from the positions indicated in the drawing, and in its first Y position the bridging member 40 connects together the stationary contacts 51 whereby a circuit is established through a conductor 52 from a selected tap on the primary winding of the transformer 17, through the bridging member and a conductor 53 to a selected tap on the reactor coil 29 and thence through the reactor coil to the common connection 3'7. For the next Y connection the bridging member 40 is moved to connect together the stationary contacts 54, whereby a circuit is established through a conductor 55 from a selected tap on the primary winding of the transformer 17, through the bridging member and a conductor 56 to a selected tap on the reactor coil 29 and thence through the reactor coil to the common connection 37. Since with this latter connection, as shown, a smaller portion of the primary winding is connected in circuit, this gives the higher of the two Y voltages. It will be understood of course that the bridging members 41 and 42 of the other two selector switches establish identical connections at the same time for the primaries of the transformers l8 and 19 respectively.

It will be observed that this switching arrangement for obtaining the various voltages with the two reactor coils is very simple and, furthermore, enables the selective adjustment of the amount of each reactor coil included in the circuit for each connection.

In the arrangement shown in Fig. 2 of the drawing, which illustrates the working of my invention in simplified form, the selector switch 58 is provided with only two closed circuit positions. When this switch is thrown toward the left from the central open circuit position shown in the drawing, the primary windings 59, 60 and 61 are connected in their entirety in delta relation with each other, the reactor coils 62, 63 and 64 being respectively included in the circuit with them. When this switch 58 is thrown from its off position toward the right, th. primary windings are connected in Y relation with each other respectively in series with the reactor coils 65, 66 and 67.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination in a polyphase furnace system, of a plurality of primary transformer windings, a secondary winding inductively associated with each of said primary windings, connections between said secondary windings and said furnace, a pair of reactance windings for each of said primary windings, and selective switching means for connecting said primary windings in delta relation with each other, each in series with one of its associated reactance windings, or for connecting said primary windings in Y relation with each other, each in series with its other reactance winding.

2. The combination in a polyphase furnace system,of a plurality of primary transformer windings, a secondary winding inductively associated with each of said primary windings, connections between said secondary windings and said furnace, a pair of reactance windings of different reactance values for each of said primary windings, and selective switching means for connecting said primary windings in delta relation'with each other, each in series with its associated reactance winding of higher reactance value or for connecting said primary winding in Y, each in series with its other reactance winding of lower reactance value.

3. The combination in a polyphase furnace system of a plurality of primary transformer windings, a secondary winding inductively associated with each of said primary windings, connections between said secondary windings and said turnace, a pair of reactance windings for each of said primary windings, permanent partial delta connections for said primary windings including one of each pair of said reactance windings, permanent partial Y connections for said primary windings including the other reactance windings, and selective switching means for completing said delta and Y connections.

EVERETT F. CHRISTENSEN. 

